I'm always open to expanding my knowledge of recycled book art. I was at the local library the other day and they had a great exhibit on folded book art that drew me in instantly. A random opportunity presented itself. The artist was having a workshop at a neighboring library just down the coast in a half hour so I sprinted over there, safely mind you. The heart book is my first attempt. Not very precise, but who cares!
Here are some expert examples by others. You could fill out the entire book with one big heart like this:
Source: Novel Brand
Celtic knot (source)
There are loads of tutorials online on how to create your own pieces, both written and video instructions, as well as patterns.
Tomorrow I'm going to a workshop at the library on origami 3D sculpture. There's always something new to learn!